This invention relates to a drafting frame for a spinning machine, particularly a regulated cotton drafting frame which has at least two consecutive roll pairs, each having a roll driven by its own electric motor as well as an electronic regulating device which regulates the rpm of at least one of the electric motors for equalizing irregularities in the sliver.
A drafting frame of the above-outlined type is described, for example, in German Offenlegungsschrift (application published without examination) No. 38 01 880. The driven rolls are associated with arresting means whose function is to prevent, during standstill, an undesired rotation of the rolls which may occur as a result of the tension of the sliver or electronic drifting or other causes.
In a drafting frame for wool in which between two roll pairs needle bars or needle rows are arranged, it is known to associate the rolls with brakes which during the startup and the stoppage are controlled by braking signals in such a manner that they disengage and, respectively, engage upon predetermined braking signals. Such an arrangement is disclosed in European Patent No. 141,505.
In drafting frames for ring spinning machines which have long lower rolls extending in the longitudinal direction of the machine, it is known--as disclosed in Published European Application No. 327 921--to provide, between the drive motors, a reverse rotation preventing pawl-and-ratchet assembly for a driven lower middle roll and for a driven lower delivery roll. Such a construction is to prevent, during standstill, the decay of the torsion effect which has been built up during operation to thus avoid drafting errors. In the freewheeling run the pawl slides over the tips of the ratchet teeth which results in wear. The ratchet is capable of moving in the reverse direction through the maximum tooth division so that a reverse turning of the roll during standstill cannot be entirely prevented.